Jangaplanet is correct and also know that using the amazon capsule is the only way you can display Amazon ads on your hubs.
There is also an option for adding products manually one-by-one rather than using search. The search feature doesn't always show you relevant items.
To add them one-by-one, go to amazon.com, search for products, click on a product, and copy the entire url from your browser's address bar and paste in to the Amazon capsule. The only time I see this having trouble is when the item doesn't have a picture on amazon.
You can also choose to have the capsule on the right side or choose to have it across your entire text area. If it's on the right, you can choose to have display as gray, blue, or white.
Another option is you can have it display anywhere from 1 to 10 items per capsule. If you need more, you can just add another capsule and the reader really shouldn't notice any breaks between them (as in it appears as one continued, blended section).